Shared access networks such as cable television systems, the so-called ‘wireless cable’ systems, and power line data networks are now common. Cable systems are typically comprised of a central controller (referred to as a “headend”) with one or more trunk lines extending therefrom. A series of feeder lines extends from each trunk into subscriber areas. Service lines run from the feeder lines to individual dwellings. The trunk, feeder lines, and service lines may be either fiberoptic or coaxial cable, or a combination of both. Each subscriber is attached via a line tap onto the feeder or service line. This permits users to freely access the data carried by the cable system, be it television programming or computer data.
Shared access networks may also be wireless, such as a wireless cable network. In the case of wireless cable networks, a single base station radiates and receives voice and data RF signals to and from a plurality of subscribers. In order to increase the capacity of the network without requiring additional frequency channels, the base station may use sectored antennas or multiple polarizations to decrease the number of subscribers sharing a given frequency band. However, as long as at least two subscribers share the same frequency, base station antenna sector, and polarization, then the wireless service also qualifies as a shared access medium.
Power line data and voice networks (i.e. power line multimedia networks) are examples of shared access networks. Subscribers share access to the power cables, much as cable subscribers share access to the coaxial cable signals. The power line signals may further be shared in that signals from a group of subscribers may be collected and transmitted to the service provider by wireless base stations in the neighborhood, and these base stations may also share bandwidth with other base stations prior to reaching the service provider's headend (or central controller) facility.
While shared access networks allow a phenomenal number of people access to information, they suffer problems in transmitting this information. When voice and data traffic are sent over such networks, they are often kept separate, usually via different frequency allocations, and often by using different physical and media access control (MAC) protocols. While less efficient and more costly to deploy, the separation of voice and data permit the quality requirements of voice traffic to be guaranteed, regardless of the data traffic load at any given instant.
Modern networks are emerging which integrate voice and data traffic. Thus, the two services share the overall bandwidth available. Such multimedia networks take the approach that voice packet data are formatted and transmitted in the same manner as data packets over the network. Asynchronous Transfer Mode (ATM) systems and internet protocol (IP) systems employ this approach. However, to ensure that voice packets are transmitted in a timely manner, bandwidth must be reserved on the network and managed by higher level entities. Further, a step called segmentation and reassembly (SAR) is required wherein large packets must be chopped up into smaller pieces for transport.
Take the example of IP voice and data transmitted over a hybrid fiber1coaxial cable network. Standards are being developed (among them Data Over Cable System Interface Specification (DOCSIS)) in order to ensure that voice traffic may be given service priority, thus theoretically preventing degradation when mixed with data traffic. However, current methods of mixing voice and data are inefficient. Additional bits must be sent for each voice packet when compared to traditional time domain multiplexing (TDM), which is employed to transmit voice over circuit switched networks such as the public switched telephone network. Further, when technologies such as voice activity detection (VAD) are used, the voice traffic may still suffer under heavy data loading unless additional measures are taken.
Accordingly, there is a need for a more efficient system and method of mixing data and voice communications over a shared access network.